This invention relates to sealing discontinuities, for example, of the type found in motor vehicles.
Motor vehicles such as automobiles and trucks have metal surfaces that are typically painted "on-line" using an electrostatic spray process. The paints used are relatively brittle because they are formulated to be hard, durable and to approximate the low coefficient of thermal expansion characteristic of metal surfaces.
These motor vehicles also have joints that must be sealed. One example is a generally non-planar overlap joint formed by welding together the roof and side panel of the vehicle to create a U-shaped trough called a roof ditch. Water collects in the roof ditch and then is drained away from the vehicle.
To prevent water from seeping through the joint it is necessary to seal it. It is often difficult to obtain a good seal, however, because the joint is not planar. In addition, the width of the roof ditch typically varies along its length, further complicating the ability to provide a good seal.
In practice, roof ditch joints are typically sealed using a paste-like plastisol which is then painted, baked and cooled to room temperature. The surface of the sealant may be covered with a plastic or rubber molding having a flexible top surface, which molding may be painted, for example to match or complement the color of the vehicle exterior. Alternatively, a metal molding may be used. The molding is typically attached to the sealant surface using a mechanical fastener or a pressure sensitive adhesive.
The plastic or rubber molding cannot be painted "on-line" along with the rest of the vehicle because the brittle, electrostatically applied paint will crack and flake off the surface owing to poor adhesion and a mismatch in the coefficients of thermal expansion between the molding surface and the paint. Therefore, the plastic or rubber molding is painted "off-line" in a separate operation using specially formulated paints.